NORMAL VALUES FOR THE NUCHAL TRANSLUCENCY

AND THE TECHNIQUE FOR MEASUREMENT

 

Criteria to maximize good quality of NT ultrasound

  1. NT ultrasound should only be performed by sinologist / sonographers certified in the technique.
  2. Transabdominal or transvaginal approach should be left to the sinologist / sonographer's discretion, based on maternal body habitus, gestational age, and fetal position.
  3. Gestation should be limited between 10 and 14 weeks (Crown Rump Length (CRL) 36 to 80 mm).
  4. Fetus should be examined in a mid-sagittal plane.
  5. Fetal neck should be in a neutral position.
  6. Fetal image should occupy at least 75% of the viewable screen.
  7. Fetal movement should be awaited to distinguish between amnion and overlying fetal skin, because, at this gestation, both structures appear as thin membranes. This is achieved by waiting for spontaneous fetal movement away from the amniotic membrane or by manually bouncing the fetus off the amnion.
  8. Calipers should be placed on the inner borders of the nuchal fold.
  9. Calipers should be placed perpendicular to the fetal body axis.
  10. At least three NT measurements should be obtained, with the mean value of those used in risk assessment and patient counseling.

 

 

Nuchal Cord

 

Note the different thickness of the nuchal translucency above and below the nuchal cord

 

 

 

Normal nuchal translucency

Increased nuchal translucency – Normal Karyotype

 

Increased nuchal translucency – Down Syndrome

Increased nuchal translucency – Trisomy 18

 

 

 

REFERENCES

  1. Panyada PP, Altman D, Brizot ML et.al. Repeatability of measurement of fetal nuchal translucency thickness. Ultrasound Obstet Gynecol 1995;5:337-340.
  2. Malone FD, D'Alton ME. Fetal nuchal fold translucency screening. Contemporary OB-GYN 1998;43:117-131.
  3. Whitlow BJ, Chatzipapas I, Economides DL. The effect of fetal neck position on nuchal translucency measurements. Br J Obstet Gynaecol 1998;105:872-876.